Fluidized bed reaction system and method of producing titanium tetrachloride

ABSTRACT

This disclosure relates to a fluidized bed reaction system and method for continuous production of titanium tetrachloride from titanium-bearing materials containing high concentrations of alkaline earth metal impurities. Agglomerated heavy particles in a reaction are taken out continuously from a chlorination reactor without clogging and stopping. The reactors and related methods disclosed apply to the chlorination of titanium slag containing high content of alkaline earth metal oxides of up to 15% by weight.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND Field

The disclosure relates to a fluidized bed reactor for producing titaniumchloride from titanium-bearing slags.

Description of the Related Art

Titanium tetrachloride can be prepared from chlorination oftitanium-bearing raw material in a reducing atmosphere via acarbochlorination reaction. Carbochlorination is a high temperature(800-1000° C.) reaction performed in the presence of Cl₂ gas andpetroleum coke as a reducing agent. The chlorinator applies eitherfixed-bed chlorination or fluidized bed chlorination methods.

In a fixed-bed chlorination method, ground, powdered titanium-bearingraw material is mixed with petroleum coke and a binder, and is formedinto briquettes. Fixed-bed chlorination methods are rarely used todaydue to low reaction rate and low heat transfer efficiency. Influidized-bed chlorination methods, titanium-bearing raw material andcoke are fluidized by Cl₂ and other process gases associated with acarbochlorination reaction. Titanium-bearing slag has 65-95% TiO₂ as amajor component and other minor components (Fe₂O₃, MgO, CaO, SiO₂,Al₂O₃).

Presently, only titanium slag having a content of MgO and CaO less than0.1% is acceptable as a feedstock for continuous TiCl₄ production influidized-bed carbochlorination commercial plant.

SUMMARY

Disclosed herein is a fluidized bed reactor configuration and relatedmethods that enable continuous production of titanium tetrachloride fromtitanium-bearing materials containing high concentrations of alkalineearth metal impurities through fluidized-bed carbochlorination.

One aspect of the invention provides a titanium chlorination fluidizedbed reaction system. The system comprises: a reaction vessel lined witha refractory material configured to withstand a high temperatureenvironment of over 1000° C. for running the following reaction therein:TiO₂+2Cl₂+C→TiCl₄+CO/CO₂; a baseplate providing a base for the reactionvessel and comprising a center portion and a rim portion around thecenter portion, the center portion comprising a recessed center surface,the rim portion comprising a rim surface that is elevated from therecessed center surface; a collection zone being a space defined by therecessed center portion of the baseplate and configured for collectingthe agglomerated particles containing high content of molten alkalineearth metal chlorides while running the reaction in the reaction vessel;a reaction zone being a space is above the collection zone and the rimsurface, in which the reaction is occurring primarily within thereaction vessel; a plurality of rim nozzles formed through the rimsurface of the baseplate and configured for supplying fluidizing gasdirectly into the reaction zone; a plurality of center nozzles formedthrough the recessed center surface of the baseplate and configured forsupplying fluidizing gas into the reaction zone via the collection zone;and a gas flow control for controlling flow of the fluidizing gas to theplurality of rim nozzles and to the plurality of center nozzles, whereinthe system is configured to control a linear fluidizing velocity of thefluidizing gas supplied through the plurality of center nozzles to besubstantially lower than a linear fluidizing velocity of the fluidizinggas supplied through the plurality of rim nozzles when the system isrunning for the chlorination reaction in the reaction vessel.

In the foregoing system, the system is configured to control the linearfluidizing velocity of the fluidizing gas supplied through the pluralityof center nozzles to be about 30% to about 90% of the linear fluidizingvelocity of the fluidizing gas supplied through the plurality of rimnozzles. The system may further comprise a discharge outlet in fluidcommunication with the recessed center portion of the baseplate andconfigured for discharging substances collected in the collection zone.The system may further comprise a discharge control configured tocontrol the discharge outlet either continuously or intermittently.

Still in the foregoing system, the baseplate may further comprise adegasifying section further recessed from the recessed center portionfor temporarily storing the agglomerated particles containing highcontent of molten alkaline earth metal chlorides from the collectionzone and for stripping chlorine gas from the agglomerated particlescontaining high content of molten alkaline earth metal chloridestherein. The system may further comprise a purge gas supply connected tothe degasifying section for supplying the purge gas into the degasifyingsection for use in stripping chlorine gas from the agglomeratedparticles containing high content of molten alkaline earth metalchlorides. The purge gas may be selected from the group consisting ofnitrogen, argon, oxygen or a mixture of one or more of the foregoing.The degasifying section may be provided between the collection zone andthe discharge outlet such that substances after degasifying are to bedischarged through the discharge outlet.

Still in the foregoing system, the system may further comprise a firstmanifold and a second manifold, wherein the first manifold is connectedto the plurality of rim nozzles for supplying the fluidizing gas to theplurality of rim nozzles, wherein the second manifold is connected tothe plurality of center nozzles for supplying the fluidizing gas to theplurality of center nozzles. The gas flow control may comprise aplurality of gas flow regulators for regulating gas flow to each of theplurality of rim nozzles and the plurality of center nozzles. Each ofthe plurality of rim nozzles has a first aperture size and each of theplurality of center nozzles has a second aperture size, wherein thefirst aperture size may be smaller than the second aperture size.

Another aspect of the invention provides a method of producing titaniumtetrachloride. The method comprises: providing the foregoing system;introducing TiO₂-containing slag into the reaction vessel; introducingfluidizing gas comprising chlorine gas into the reaction vessel throughthe plurality of rim nozzles and the plurality of center nozzles forrunning the reaction within the reaction vessel, wherein a linearfluidizing velocity of the fluidizing gas supplied through the pluralityof rim nozzles is substantially higher than a linear fluidizing velocityof the fluidizing gas supplied through the plurality of center nozzlessuch that particles containing high content of molten alkaline earthmetal chloride settle into the collection zone; and dischargingsubstances from the collection zone through the discharge outlet.

In the foregoing method, the system may comprise a discharge controllerfor controlling operation of the discharge outlet, wherein dischargingof the substances is performed continuously or intermittently. Thebaseplate may further comprise a degasifying section further recessedfrom the recessed center portion, wherein the system may furthercomprise a purge gas supply connected to the degasifying section,wherein the method may further comprise: introducing the purge gas intothe degasifying section and stripping at least part of chlorine gas fromthe agglomerated particles containing high content of molten alkalineearth metal chlorides that has settled in the collection zone andtransferred into the degasifying section from the collection zone.

Still in the foregoing method, the purge gas may be selected from thegroup consisting of nitrogen, argon, oxygen or a mixture of one or moreof the foregoing. The degasifying section may be provided between thecollection zone and the discharge outlet, wherein substances afterdegasifying are discharged through the discharge outlet. The method mayfurther comprise a first manifold and a second manifold, wherein thefirst manifold is connected to the plurality of rim nozzles forsupplying the fluidizing gas to the plurality of rim nozzles, whereinthe second manifold is connected to the plurality of center nozzles forsupplying the fluidizing gas to the plurality of center nozzles, whereinthe gas flow control comprises a plurality of gas flow regulators forregulating gas flow to each of the plurality of rim nozzles and theplurality of center nozzles.

Still in the foregoing method, each of the plurality of rim nozzles hasa first aperture size and each of the plurality of center nozzles has asecond aperture size, wherein the first aperture size may be smallerthan the second aperture size. The linear fluidizing velocity of thefluidizing gas supplied through the plurality of center nozzles may beabout 30% to about 90% of the linear fluidizing velocity of thefluidizing gas supplied through the plurality of rim nozzles. TheTiO₂-containing slag may comprise alkaline earth metal oxide in anamount from about 0.1 wt % to about 15 wt %. The TiO₂-containing slagmay comprise alkaline earth metal oxide in an amount from about 3 wt %to about 8 wt %. The molten alkaline earth metal chlorides in thefluidized bed may be maintained at a concentration between 5 wt % and 20wt %.

Some embodiments relate to a fluidized bed reactor comprising: (a) areaction zone chamber comprising: (i) an entry port configured to inputslag into the reaction zone chamber, and (ii) a bottom surface of thereaction zone chamber comprising first nozzles configured to deliver afluidizing gas to the reaction zone chamber at a first linear fluidizingvelocity; (b) a lower collection chamber comprising a bottom surfacecomprising second nozzles configured to deliver the fluidizing gas tothe lower collection chamber at a second linear fluidizing velocity,wherein the nozzles are configured so that the first superficialvelocity of fluidizing gas introduced into the reaction zone is fasterthan the second superficial velocity of fluidizing gas introduced intothe lower collection chamber; (c) an outlet pipe comprising a first endthat is connected to the bottom surface of the lower collection chamber,wherein the outlet pipe is configured to remove agglomerated particlesthat collect in the lower collection chamber; (d) a bottom degasifiersection connected to a second end of the outlet pipe, wherein thedegasifier section is configured to strip fluidizing gas fromagglomerated particles removed from the collection chamber through saidoutlet pipe by streaming the slag with a purge gas; and (e) a returnport connected to the reaction zone chamber, configured to return washedslag back into the reaction zone chamber.

In some embodiments, the fluidizing gas is chlorine gas and the purgegas is nitrogen gas. In some embodiments, the fluidized bed reactorfurther comprises an upper disengagement section configured to reduce alinear fluidizing velocity of product gases from the reaction zone. Insome embodiments, the upper disengagement section is sized to reduce thesuperficial velocity of product gases leaving the middle reaction zoneto 0.03 m/s to 0.10 m/s. In some embodiments of fluidized bed reactorsdisclosed herein, the nozzles are configured to deliver a fluidizing gasto the reaction zone chamber and the collection chamber are configuredso that the linear fluidizing velocity delivered to the collectionchamber is between about 30% and about 90% of the linear fluidizingvelocity delivered to the reaction zone.

In some embodiments, hole sizes of nozzles configured to deliver afluidizing gas to the reaction zone chamber are smaller than hole sizesof nozzles configured to deliver fluidizing gas to the collectionchamber. In some embodiments, the fluidized bed reactor furthercomprises an isolation valve on the outlet pipe, wherein a section ofthe outlet pipe downstream of the isolation valve is isolated from thecollection chamber when the isolation valve is closed or whereinagglomerated particles that have accumulated in the collection chamberare able to pass through the outlet pipe.

Some embodiments relate to a process for continuous production oftitanium tetrachloride from titanium-bearing slag containing highconcentration(s) of alkaline earth metal(s) in a fluidized bed reactoras disclosed herein, comprising: (a) introducing TiO₂ containing slaginto the fluidized bed reactor; (b) introducing a chlorine gas throughthe nozzles in the bottom of the reaction zone chamber and throughnozzles in the bottom surface of the lower collection zone chamber,wherein the linear fluidizing velocity of gas introduced through thenozzles in the bottom of reaction zone chamber is higher than the linearfluidizing velocity of the gas introduced into the lower collection zonechamber; (c) allowing agglomerated particles of slag to settle into thecollection chamber; (d) drawing agglomerated particles periodically fromthe collection chamber through the output pipe; (e) stripping fluidizinggas from agglomerated particles removed from the collection chamberthrough said outlet pipe by streaming the agglomerated particles with apurge gas; and (f) leaching alkaline earth metal chlorides in theagglomerated particles away from solid bed particles by dissolving withwater.

In some embodiments, the linear fluidizing velocity of the fluidizinggas introduced into the lower collection chamber is 30%-90% of thelinear fluidizing velocity of the fluidizing gas introduced into thereaction zone chamber. In some embodiments, the amount of magnesiumoxide and/or calcium oxide present in the slag is 0.1-15% by weight. Insome embodiments, the amount of magnesium oxide and/or calcium oxidepresent in the slag is 0.2-6% by weight. In some embodiments, the amountof magnesium oxide and/or calcium oxide present in the slag is 0.5-6% byweight. In some embodiments, the amount of magnesium oxide and/orcalcium oxide present in the slag is 1.5-6% by weight. In someembodiments, the fluidizing gas is nitrogen, argon, chlorine, oxygen ora mixture thereof.

In some embodiments, the nozzles in the bottom of the reaction zonechamber and in the bottom surface of the lower collection zone areassociated with flow regulators that equalize the flow rate of thefluidizing gas passing through each of the nozzles. In some embodiments,hole sizes of nozzles configured to deliver a fluidizing gas to thereaction zone chamber are smaller than hole sizes of nozzles configuredto deliver fluidizing gas to the collection chamber. In someembodiments, the concentration of molten alkaline earth metal chloridesin the fluidized bed is maintained between 5% and 20% by weight. In someembodiments, the concentration of molten alkaline earth metal chloridesin the fluidized bed is maintained between 6% and 8% by weight. Someembodiments of the process further comprise a step of returning washedbed particles back into the fluidized bed reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of some embodiments are found in the accompanyingdrawings:

FIG. 1 is a schematic process diagram in accordance with an embodimentof the invention.

FIG. 2 illustrates a fluidized-bed reactor for titanium chlorination inaccordance with an embodiment of the invention.

FIG. 3 illustrates a lower portion of the reactor of FIG. 2 inaccordance with an embodiment of the invention.

FIG. 4 is a plan view of the baseplate and the refractory-lined walls ofthe reactor of FIG. 2 in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Certain embodiments of the invention will now be described withreference to the accompanying drawings. The terminology used in thedescription presented herein is not intended to be interpreted in anylimited or restrictive manner, simply because it is being utilized inconjunction with a detailed description of certain specific embodimentsof the invention. Furthermore, embodiments of the invention may includeseveral novel features, no single one of which is solely responsible forits desirable attributes or which is essential to practicing theembodiments herein described.

Titanium Chlorination Reaction

According to an embodiment of the invention, titanium tetrachloride(TiCl₄) is produced through by chlorinating titanium oxide in afluidized-bed reactor.TiO₂+2Cl₂+C→TiCl₄+CO/CO₂

Titanium oxide reacts with chlorine and carbon in the form of petroleumcoke (used for its low ash and hydrogen content) in a fluidized bed at1,000° C. to make TiCl₄ and CO/CO₂. The reaction is fast and exothermic,providing enough heat to be self-sustaining.

According to an embodiment, titanium-bearing slag (with particle sizesimilar to sand) and petroleum coke (with about five times biggerparticle size than titanium-bearing slag) are supplied to thefluidized-bed reactor. In embodiments, titanium-bearing slag has 65-95%TiO₂ as a major component and other minor components (Fe₂O₃, MgO, CaO,SiO₂, Al₂O₃).

More than 95% of TiO₂ in slag is converted into TiCl₄, which then leavesthe chlorinator along with CO and CO₂ gases. Hot TiCl₄ leaving thechlorinator is condensed and separated from the CO and CO₂. TiCl₄produced from titanium minerals may be oxidized to produce TiO₂ for usein the pigment industry. The resulting TiO₂ produced may be treated withorganic and inorganic compounds to enhance surface properties of thepigment.

Fluidized Bed Chlorination Reaction System

Referring to FIG. 2 and FIG. 3, a refractory reactor 60 includes fourreactor sections: top disengagement section 40, middle reaction zone 30,lower collection zone 20, and a bottom degasifier section 10, which willbe discussed further below. In embodiments, the reactor 60 hasrefractory-lined walls and a baseplate 70 that defines the inner spaceand sections. Baseplate 70 defines the bottom, horizontal surfaces ofthe middle reaction zone 30 and the lower collection zone 20. Thereaction zone 30 has a generally-cylindrical space defined by therefractory-lined walls and the baseplate.

The penetrations through the bottom of the collection zone 20 includethe degasifier section 10 and gas inlets 23 for supplying chlorineand/or other process gases to fluidize and cool the bed residue.Penetrations through the side of the reaction zone 30 includes a freshfeed inlet 32 for supplying the feed mixture of coke and slag to thebed, a recycle feed inlet 33 for supplying the recovered feed to thereaction zone 30, and an instrument insert 34 for insertinginstrumentation into the reaction zone 30 to monitor the condition ofthe fluidized-bed. Penetrations through the bottom of the reaction zone30 include gas inlets 35 for supplying chlorine and/or other processgases to fluidize and react with the coke and metal oxides in the bed.Penetrations through the top and sides of the disengagement section 40provide a discharge outlet 42 for discharging the reaction results orproduct gases, a coolant inlet 43 for supplying liquid titaniumtetrachloride as coolant, and an instrument insert 44 for insertinginstrumentation to monitor the operation. Although not shown, apenetration may be formed through the refractory walls of the reactionzone 30 for use in cleaning the reaction zone 30.

Referring to FIG. 1 and FIG. 2, a mixture of slag and coke is fed intothe reaction zone 30 through the fresh feed inlet 32 while chlorine gasis fed into the reactor 30 through the gas inlets 23 and 35 to fluidizethe reaction bed and react with the coke and metal oxides in the slag.The product gases leave the reactor through the disengagement section40. Product gases containing metal chloride vapors leave the top of thereactor 60 with entrained solid from the fluidized bed. Product TiCl₄gases are captured by condensation, whereas carbon dioxide, carbonmonoxide and nitrogen gas are released. Titanium tetrachloride isseparated from the solid and waste gases and recovered as a liquid forpurification. Unreacted residue and metal chlorides may be recycled.

Alkaline Earth Metal Oxides

During the carbochlorination reaction, alkaline earth metal oxides (MgO,CaO) are easily converted into MgCl₂ and CaCl₂), which disadvantageouslyaccumulate in a molten state in the bed due to low volatility. Thesemolten salts, when coated on particle surfaces, prevent chlorine gascontact needed for further reaction, and they accelerate agglomerationof solid particles, resulting in immobilization and plugging of thereaction bed. For a continuous operation, the amount of solidagglomerates must be controlled inside the reactor. In the prior art,most commonly the solid agglomerates or spent bed residues are removedfrom the reactor periodically. To do so, the reactor must be shut down,and a continuous operation for a long period is difficult. For a longercontinuous operation without a stop, the content of MgO and CaO needs tobe lower. Fluidized bed reactors and methods of the prior art requirethe use of titanium slag that contains low levels of MgO and CaO. Incertain operations of prior art reactors, the concentration of MgO inthe feed stock is limited to an amount of 1.5% or less, and theconcentration of CaO is limited to an amount of 0.2% or less. This meansthat titanium slags having a higher amount of MgO and/or CaO would notbe acceptable for these prior art reactors.

Continuous Operation of Reactor by Discharging MgCl₂ and CaCl₂

According to embodiments of the present invention, a continuousoperation of a fluidized bed chlorinator can be accomplished withoutfrequent interruptions for removal of spent bed residue even when theconcentration of MgO and CaO is high in the feed stock. In embodiments,the reactor 60 includes collection zone 20 under reaction zone 30. Forcollection zone 20, in one embodiment, the baseplate 70 is recessed inits central area. In embodiments, the linear fluidizing velocity of gassupplied into the reactor 60 is controlled such that the linearfluidizing velocity at nozzles 25 of the baseplate 70 in the recessedcollection zone 20 is lower than the linear fluidizing velocity atnozzles of the baseplate 70 outside the collection zone 30. Inembodiments, the agglomerated particles containing high content ofmolten alkaline earth metal chlorides (MgCl₂ and CaCl₂)) are collectedin the collection zone 20 and discharged from the reactor 60 through adischarge outlet provided in or next to the collection zone 20 while thereactor 60 is running without having to shut down its operation for anextended period of time.

Fluidized Bed Reactor

In embodiments, the fluidized bed reactor 60 is typically a verticalcarbon steel pressure vessel, with castable refractory-lined walls orlined with bricks to withstand high temperature and a chlorineenvironment required to convert TiO₂, Fe₂O₃, MgO, CaO, Al₂O₃ in slag totheir respective chlorides. Referring to FIG. 2, the refractoryfluidized bed reactor 60 includes a reaction zone, which includes amiddle reaction zone 30 and a lower collection zone 20. The reactor 60further includes an upper disengagement zone 40 and is lined with bricks75. The diameters and heights of these upper three sections of thereactor are determined by the operating conditions of the process andthe desired production capacity.

Middle Reaction Zone

In embodiments, a mixture of coke and slag are fed into the middlereaction zone 30 and ignited. Gas distribution manifolds located at thebottom of the middle reaction zone are configured to feed chlorine gasinto the bed, thereby fluidizing the bed. The carbochlorination reactionoccurs primarily in the middle reaction zone, at high temperaturesbetween 800° C. to 1000° C. The fluidized bed mixture of coke and slagsolid reactants is contained in the reaction zone. The height of thereaction zone is adequate to contain the necessary amount of solidreactants to maintain the chlorine conversion efficiency above 95%.

Upper Disengagement Zone

In embodiments, product gases containing TiCl₄ enter the upperdisengagement zone 40. The upper disengagement zone 40 serves to reducethe velocity of product gases leaving the reaction zone to between 0.03m/s and 0.10 m/s. This minimizes solid particulate entrainment in thegas stream leaving the reactor through port 42. Titanium tetrachloridecoolant is added through a port 43 to the upper disengagement zone tomaintain the temperature of the exiting gases between 800° C. and 1000°C.

Lower Collection Zone

In embodiments, the lower collection zone 20, which is located at thebottom center of the reactor, is specially designed to allow largeragglomerated particles in the hot bed to accumulate. In someembodiments, the lower boundary of the lower collection zone 20 islocated below the lower boundary of the middle reaction zone 30. Inother embodiments, the lower collection zone 20 may be sequestered fromthe bottom of the middle reaction zone 30 by a physical barrier.Accumulation of the agglomerated particles in the lower collection zone20 is promoted by delivering chlorine gas at different linear velocitiesto the middle reaction zone 30 and the lower collection zone 20 throughtwo gas distribution manifolds.

Gas Distribution Manifolds

In embodiments, the reaction zone gas distribution manifold is locatedat or under the bottom of the middle reaction zone 30, and a lowercollection zone gas distribution manifold is located at or under thebottom of the lower collection zone 20. Both manifolds contain aplurality of nozzles 25, which are distributed evenly across thebaseplate 70 and configured to deliver chlorine gas into the bottom ofthe middle reaction zone 30 and the lower collection zone 20,respectively.

In embodiments, separate gas distribution manifolds are designed toprovide different uniform flow rates into the bottoms of the reactionzone 30 and collection zone 20 to fluidize the reaction bed. Inembodiments, chlorine and other process gases are introduced into thegas distribution manifolds which provide controlled gas flows throughthe pipes 12 going through the refractory base to the reaction zone 30and the pipes 13 going to the lower collection zone 20. In someembodiments, gas flow to each nozzle through the pipes 12 and 13 iscontrolled using gas flow regulators or control valves such that thepressure drop across multiple nozzles connected to pipes 12 and 13 isabout the same. In embodiments, the gas flow regulators or controlvalves are controlled by a computerized flow control.

Nozzles

FIG. 3 and FIG. 4 provide detailed schematic diagrams of someembodiments. Fluidizing gas is introduced into reactor through nozzlesor bubble caps 25, which are evenly distributed on the bottoms of themiddle reaction zone 30 and the lower collection zone 20. The nozzlesdepicted in FIG. 4 are arranged on baseplate 70 in concentric circularpatterns, with representative nozzles shown. In other embodiments, thenozzles may be arranged in other pattern formations resulting in an evendistribution of the nozzles across the baseplate 70. The nozzles thatare formed through the central recessed surface of the baseplate 70 feedchlorine gas directly to the lower collection zone 20. The nozzles thatare formed through the outer rim surface of the baseplate 70 feedchlorine gas directly to the middle reaction zone 30.

Velocity Difference by Nozzles

In embodiments, the linear velocity at the nozzles feeding into thelower collection zone 20 is lower than the linear velocity at thenozzles feeding into the middle reaction zone 30. In embodiments, theaperture size of the nozzles formed through the central recessed surfaceof the baseplate 70 (feeding directly into the lower collection zone 20)are the same. In embodiments, the aperture size of the nozzles formedthrough the outer rim surface of the baseplate 70 (feeding directly intothe middle reaction zone 30) are the same. In some embodiments, theaperture size for nozzles feeding into the collection zone 20 is largerthan the aperture size for nozzles that feed into the reaction zone 30to provide the differential gas velocities in the middle reaction zone30 compared to the lower collection zone 20. This velocity differencedrives larger agglomerate particles having higher concentrations ofalkaline earth metal chlorides to accumulate in the lower collectionzone 20 by gravity.

The lower linear fluidizing velocity in the collection zone 20 causescontinuous elutriation of agglomerated solid particles from thefluidized bed in the reaction zone 30 into the collection zone 20, whichis followed by subsequent removal of the particles from the collectionzone 20 of the reactor. Ultimately, the water-soluble alkaline earthmetal chlorides remaining in the agglomerated particles in thecollection zone 20 are removed, and solid particles without alkalineearth metal chlorides are fed as a recovered feed. Moreover, because ofthe cooling effect of introducing chlorine gas into the collection zone20, the agglomerated solid particles are advantageously cooled relativeto the temperature of the reaction zone 30.

Degasifier Section

In embodiments, a degasifier section 10 is contiguous with the lowercollection zone 20. A portion of the accumulated particles in collectionzone 20 fills the degasifier section 10 and is removed through thedouble-locked discharge pot 50 to maintain the concentration of themolten alkaline earth metal chlorides in the bed between 6% and 8% byweight.

Cold nitrogen gas is fed into the degasifier section 10 to stripchlorine from agglomerated particles collected in the lower collectionzone 20. Also agglomerated particles are cooled in the collection zone20 by the cold chlorine gas, which facilitates the agglomeratedparticles to settle into and remain in the collection zone 20.

Referring to FIG. 2 and FIG. 3, the outlet pipe 22 of the degasifiersection 10 is connected to the isolation valve at the inlet to thedischarge pot or double-lock discharge pot 50. Nitrogen gas 51, 52 isadded to outlet pipe of the degasifier section 10 just above theisolation valve. A constant flow of nitrogen gas strips and returns thechlorine from the bed residue in the degasifier section and through thecollection zone 20 to the middle reaction zone 30 of the chlorinator 60.The bed residue drops into the double-lock discharge pot 50 which feedsthe solid to recovery process 53.

Solid Recovery

Agglomerated particles collected in the lower collection zone 20 areremoved either continuously or intermittently upon opening of a valvedownstream of the collection zone. The particles flow through the valveto a solid recovery process. In some embodiments, a double-lockdischarge pot 50 collects the solid, which are easily and safelytransferred to the solid recovery process 53.

In some embodiments, bed residue removal rate is controlled by operationof double-lock discharge pot 50. The frequency of filling anddischarging of the double lock pot 50 controls the amount of the bedremoval. The residue in the double-lock discharge pot 50 is dischargedto Storage Hoppers. The agglomerated particles are cooled and fed to anagitated vessel, where the alkali earth metal chlorides such as CaCl₂)and MgCl₂ are dissolved in water. The slurry is filtered and thecollected solid is washed. The washed solid containing mainly slag andcoke is dried in a rotary dryer before they are recycled to thechlorination reactor 60 through a nozzle located at the side of thereaction zone 33. The filtrate is neutralized and discharged to a plantwaste water treatment facility.

Different Linear Fluidizing Velocities in the Reaction Zone and theCollection Zone

In embodiments, the lower collection zone 20 is centered below thereaction zone 30 in a fluidized bed reactor. Separate gas distributionmanifolds for the middle reaction zone 30 and the lower collection zone20 allow different linear fluidizing velocities in the middle reactionzone and the lower collection zone. In particular, the linear fluidizingvelocity in the collection zone 20 is lower than the correspondinglinear fluidizing velocity in the reaction zone 30.

Linear Fluidizing Velocity in Collection Zone

In embodiments, the differential linear fluidizing velocities in thereaction zone 30 and the collection zone 20 are set or adjusted topermit agglomerated particles to settle into the collection zone 20. Inembodiments, the linear fluidizing velocity of gas entering the reactionzone 30 through nozzles outside of the collection zone typically rangesfrom about 0.09 m/s to about 0.37 m/s.

In embodiments, the linear fluidizing velocity at nozzles in thecollection zone 20 typically ranges from about 0.02 m/s to about 0.34m/s, and allows larger agglomerated bed material to accumulate in thecollection zone. In some embodiments, the linear fluidizing velocity atthe nozzles in the lower collection zone 20 is about 0.02 m/s, about0.03 m/s, about 0.04 m/s, about 0.05 m/s, about 0.06 m/s, about 0.07m/s, about 0.08 m/s, about 0.09 m/s, about 0.10 m/s, about 0.11 m/s,about 0.12 m/s, about 0.13 m/s, about 0.14 m/s, about 0.15 m/s, about0.16 m/s, about 0.17 m/s, about 0.18 m/s, about 0.19 m/s, about 0.20m/s, about 0.21 m/s, about 0.22 m/s, about 0.23 m/s, about 0.24 m/s,about 0.25 m/s, about 0.26 m/s, about 0.27 m/s, about 0.28 m/s, about0.29 m/s, about 0.30 m/s, about 0.31 m/s, about 0.32 m/s, about 0.33m/s, about 0.34 m/s, or the linear fluidizing velocity in the collectionzone is within a range bounded by any two of the preceding numericalvalues.

Linear Fluidizing Velocity Differential

In embodiments, the linear fluidizing velocities at nozzles in thecollection zone 20 and the middle reaction zone 30 are set or adjustedsuch that the linear fluidizing velocity in the collection zone 20 issubstantially lower than the linear fluidizing velocity in the reactionzone 30. In this context, the term “substantially lower” means that thelinear fluidizing velocity in the collection zone 20 is lower than thelinear fluidizing velocity in the reaction zone 30 by at least 10%.

In some embodiments, the linear fluidizing velocities at nozzles in thecollection zone 20 and the middle reaction zone 30 are set or adjustedsuch that the linear fluidizing velocity in the collection zone 20 isabout 30% to 90% of the linear fluidizing velocity in the reaction zone30 (i.e., the linear fluidizing velocity in the collection zone is about10% to about 70% lower than the linear fluidizing velocity in thereaction zone). In some embodiments, the lower linear fluidizingvelocity in the collection zone 20 about 30%, about 35%, about 40%,about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about75%, about 80%, about 85% or about 90% of the velocity in the reactionzone. Depending on the desired linear fluidizing velocity in thecollection zone, the linear velocity of the fluidizing gas introducedinto the reaction zone is adjusted accordingly higher.

Linear Fluidizing Velocity Differential for Collecting Particles ofCertain Sizes

In some embodiments, the linear fluidizing velocities are adjusted sothat particles having a diameter less than 1 mm collect in thecollection zone. In some embodiments, the particles that settle into thecollection zone are about 0.5 mm, about 0.6 mm, about 0.7 mm, about 0.8mm or about 0.9 mm in diameter. In other embodiments, particles havingdiameters of greater than 1 mm collect in the collection zone. In someembodiments, the conditions are adjusted so that particles havingdiameters of up to about 2 mm, about 3 mm, about 4 mm, about 5 mm, about6 mm, about 7 mm, about 8 mm, about 9 mm or about 10 mm collect in thecollection zone. In some embodiments, the agglomerated particles have arange of diameters, wherein the range is bounded by any two of thepreceding numerical values.

Content of Alkaline Earth Metal Oxides

According to embodiments, the amount of magnesium oxide and/or calciumoxide present in the slag, while still allowing continuous production ofTiCl₄ from the slag, may be about 0.1 wt % to about 15 wt % by weight.In some embodiments, each of magnesium oxide and calcium oxide is in theamount of 0.1-10 wt %, 0.2-7 wt % or 5-6 wt %. In some embodiments, eachof magnesium oxide and calcium oxide tolerated in the slag isindependently about 0.1 wt %, about 0.2 wt %, about 0.3 wt %, about 0.4wt %, about 0.5 wt %, about 0.6 wt %, about 0.7 wt %, about 0.8 wt %,about 0.9 wt %, about 1.0 wt %, about 1.5 wt %, about 2.0 wt %, about2.5 wt %, about 3.0 wt %, about 3.5 wt %, about 4.0 wt %, about 4.5 wt%, about 5.0 wt %, about 5.5 wt %, about 6.0 wt %, about 6.5 wt %, about7.0 wt %, about 7.5 wt %, about 8.0 wt %, about 8.5 wt %, about 9.0 wt%, about 9.5 wt % or about 10.0 wt %. In some embodiments, each ofmagnesium oxide and calcium oxide tolerated in the slag is independentlyin a range formed by two approximate numbers listed in the immediatelypreceding sentence. In some embodiments the amount of magnesium oxideand/or calcium oxide tolerated in the slags is within a range bounded byany two of the preceding numerical values. The tolerance for a higherconcentration of magnesium oxide and/or calcium oxide makes it possibleto use slags mined from a wider range of geographic locations, whichtends to be less expensive than slag having low magnesium oxide and/orcalcium oxide contents of less than 0.1%.

Control of Molten Alkaline Earth Metal Chlorides in the Bed

During a carbochlorination reaction, molten alkaline earth metalchlorides and nonreactive oxides accumulate in the reaction bed. Inparticular, alkaline earth metal oxides (MgO, CaO) are easily convertedinto MgCl₂ and CaCl₂), which disadvantageously accumulate in a moltenstate in the bed due to low volatility. These molten salts, when coatedon particle surfaces, prevent chlorine gas contact which is needed forfurther reaction, and they accelerate agglomeration of solid particles,resulting in immobilization and plugging of the reaction bed.

In the reactors and methods disclosed herein, the agglomerated particlesare in a fluid state, in that they are able to circulate within thereaction zone 30. As the linear fluidizing velocity of gas entering thereaction zone through the recessed portion of the baseplate 70 below thelower collection zone is lower than the linear fluidizing velocity ofgas entering the reaction zone through the outer rim of the of thebaseplate 70, the agglomerated particles preferentially settle into thelower collection zone by gravity. The agglomerated particles, which arein a fluid state, settle into the lower collection zone where they mayeither remain for a period of time in the case when the discharge outlet22 is blocked, or they may be immediately removed from the lowercollection zone if discharge outlet 22 is open.

According to embodiments, the molten alkaline earth metal chlorides areremoved and discharged from the reactor 60 by discharging theagglomerated particles containing high content of molten alkaline earthmetal chlorides. In embodiments, the discharge or removal is continuousor intermittent by controlling the valve of the discharge outlet. In oneembodiment, the intermittent discharge may occur periodic with a regularinterval. In another embodiment, the intermittent discharge may be withirregular intervals.

In some embodiments, the discharge of the agglomerated particlescontaining high content of molten alkaline earth metal chlorides iscontrolled to maintain a certain level of the molten alkaline earthmetal chlorides in the bed. In some embodiments, the concentration ofmolten alkaline earth metal chlorides in the bed is maintained betweenabout 5% and about 20% by weight. In other embodiments, theconcentration of molten alkaline earth metal chlorides in the bed ismaintained between about 5% and about 10% by weight or between about 6%and about 8% by weight. In embodiments, the concentration of moltenalkaline earth metal chlorides in the bed can be computed using theconcentration of the magnesium oxide and calcium oxide in the feed stockand other reaction conditions and parameters.

The reactors and methods disclosed herein permit continuouscarbochlorination reaction within the reactor, precluding the need toperiodically stop the reaction to purge the bed of agglomeratedparticles. As discussed, the establishment of fluid bed dynamics withinthe middle reaction zone and the lower collection zone promote settlingof agglomerated particles into the lower collection zone, where they maybe removed to prevent obstruction of the reaction bed.

EXAMPLES

The following examples are merely illustrative and are not limiting.

Example 1

A fluidized-bed chlorination reactor having a structure shown in FIG.2-FIG. 4 is employed. The reactor feed mixture consists of 86% titaniumslag and 14% coke.

The following is the composition (by weight) of the ground slag used:

TiO₂ 88.0% Fe₂O₃ 8.2% MgO 1.9% CaO 1.1% Other (SiO₂, Al₂O₃) 0.8%

At the start of a run 18,000 kg of coke is fed into the reactor. Thecoke is ignited and 50 m³/h air is added through the gas distributionmanifold to sustain the combustion of the coke. When the bed temperaturereaches 400° C., the air flow is slowly increased until the coke bed isfluidized. When the fluidized bed temperature reaches 700° C., 11,000 kgof feed is added to the bed at a constant rate maintaining the bedtemperature above 600° C. When the bed temperature reaches 800° C.,12,110 kg/h of chlorine gas and 8,350 kg/h of feed mixture is fed intothe reactor. The disengagement zone is maintained at 850° C. by addingliquid TiCl₄ coolant through the nozzle at the top of the reactor.

Calculated linear fluidizing velocities are about 0.12 m/sec in the 4.0m diameter reaction zone and 0.08 m/s in the 1.0 m diameter collectionzone. After 12 hours of operation, 2,930 kg/h of the bed is withdrawnfrom the reactor. Periodic samples of the bed are taken and analyzed foralkaline earth metal chlorides content.

Nitrogen gas is added just above the isolation valve at the end of the80 mm outlet pipe from the 0.3 m diameter degasifier section to the 0.20m³ double-lock discharge pot to purge the chlorine gas out of the bedresidue back to the reactor bed. Then, the solid in degasifier sectionare transferred by the double-lock discharge pot to the solid recoverysystem.

The solid is cooled and leached with water to remove water-solublealkaline earth metal chlorides. The leached slags are filtered anddried. 2,650 kg/h of dried slag having only 0.05 wt % alkaline earthmetal chlorides is returned to the reactor through the nozzle located atthe side of the reaction zone. The reaction proceeds for 200 hourswithout clogging and about 15,020 kg/h TiCl₄ is produced.

Example 2

A titanium slag with 80.1% TiO₂ is used in a fluidized-bed chlorinationreactor same as described in Example 1. The reactor feed mixturecomposition contains 86% titanium slag and 14% coke.

The following is the composition (by weight) of the ground slag used:

TiO₂ 80.1% Fe₂O₃ 9.8% MgO 3.7% CaO 2.2% Other (SiO₂, Al₂O₃) 4.2%

At the start of the run, 18,000 kg of coke is fed into the reactor. Thecoke is ignited and 50 m³/h air is added through the gas distributionmanifold to sustain the combustion of the coke. When the bed temperaturereaches 400° C., the air flow is slowly increased until the coke bed isfluidized. When the fluidized bed temperature reaches 700° C., 11,000 kgof feed is added to the bed at a constant rate maintaining the bedtemperature above 600° C. When the bed temperature reaches 800° C.,12,110 kg/h of chlorine gas and 8,350 kg/h of feed mixture areintroduced into the reaction zone. The disengagement zone is maintainedat 850° C. by adding liquid TiCl₄ coolant through a nozzle at the top ofthe reactor.

Calculated linear fluidizing velocities are about 0.12 m/sec in the 4.0m diameter reaction zone and 0.08 m/s in the 1.0 m diameter collectionzone. After 6 hours of operation, 2,900 kg/h of the bed is withdrawnfrom the reactor. Periodic samples of the bed are taken and analyzed foralkaline earth metal chloride content.

Nitrogen gas is added just above the isolation valve at the end of the80 mm outlet pipe from the 0.3 m diameter Degasifier Section to the 0.20m³ Double-lock Discharge Pot to purge the chlorine gas out of the bedresidue back to the reactor bed. Then the solid in degasifier section istransferred by the double-lock discharge pot to the solid recoverysystem.

The solid is cooled and leached with water to remove water-solublealkaline earth metal chlorides. The leached slags are filtered anddried. 2,620 kg/h of dried slag having only 0.05 wt % alkaline earthmetal chlorides is returned to the reactor through the nozzle located atthe side of the reaction zone. The reaction proceeds for 200 hourswithout clogging and about 13,670 kg/h TiCl₄ is produced.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of any appended claims. All figures, tables, and appendices, aswell as publications, patents, and patent applications, cited herein arehereby incorporated by reference in their entirety for all purposes.

What is claimed is:
 1. A fluidized bed reaction system comprising: areactor base comprising a center and a rim, wherein the center isrecessed relative to the rim; at least one reactor wall defining,together with the reactor base, an enclosed space comprising acollection zone and a reaction zone, wherein the collection zonecomprises a space within the recessed center of the reactor base,wherein the reaction zone comprises a space above the center and the rimof the reactor base such that the reaction zone is above the collectionzone; a plurality of center nozzles formed through the recessed centerof the reactor base and configured to supply fluidizing gas to thereaction zone via the collection zone; a plurality of rim nozzles formedthrough the rim of the reactor base and configured to supply fluidizinggas directly to the reaction zone; and a gas flow control configured tocontrol flow of the fluidizing gas to the plurality of center nozzlesand to the plurality of rim nozzles such that a linear fluidizingvelocity of the fluidizing gas supplied through the plurality of centernozzles is substantially lower than a linear fluidizing velocity of thefluidizing gas supplied through the plurality of rim nozzles.
 2. Thesystem of claim 1, wherein the rim of the reactor base and the center ofthe reactor base are both substantially horizontal.
 3. The system ofclaim 2, wherein the center is stepped down from the rim, wherein asurface connecting the center and the rim comprises a portion that isgenerally perpendicular to the center.
 4. The system of claim 2, whereinthe center of the reactor base is located in a central area of thereactor base and the rim is peripheral to the central area when viewingthe reactor base in a direction perpendicular to the center.
 5. Thesystem of claim 1, wherein the center is stepped down from the rim,wherein a surface connecting the center and the rim comprises a portionthat is generally perpendicular to the center.
 6. The system of claim 1,wherein the center of the reactor base is located in a central area ofthe reactor base and the rim is peripheral to the central area whenviewing the reactor base in a direction perpendicular to the center. 7.The system of claim 1, wherein the system is configured to control thelinear fluidizing velocity of the fluidizing gas supplied through theplurality of center nozzles to be about 30% to about 90% of the linearfluidizing velocity of the fluidizing gas supplied through the pluralityof rim nozzles.
 8. The system of claim 1, further comprising a firstmanifold and a second manifold, wherein the first manifold is connectedto the plurality of rim nozzles for supplying the fluidizing gas to theplurality of rim nozzles, wherein the second manifold is connected tothe plurality of center nozzles for supplying the fluidizing gas to theplurality of center nozzles, wherein the gas flow control comprises aplurality of gas flow regulators for regulating gas flow to at least oneof the plurality of rim nozzles and the plurality of center nozzles. 9.The system of claim 1, wherein one of the plurality of rim nozzles has afirst aperture size and one of the plurality of center nozzles has asecond aperture size, wherein the first aperture size is smaller thanthe second aperture size.
 10. The system of claim 1, further comprisinga discharge outlet in fluid communication with the collection zone andconfigured for discharging at least part of agglomerated particlescollected in the collection zone.
 11. The system of claim 10, furthercomprising a degasifying section recessed from the center and providedbetween the collection zone and the discharge outlet, wherein thedegasifying section is configured for temporarily storing theagglomerated particles from the collection zone and for stripping thefluidizing gas therefrom, wherein the system further comprises a purgegas supply connected to the degasifying section for supplying purge gasinto the degasifying section for use in stripping the fluidizing gas.12. A method of producing titanium tetrachloride, the method comprising:introducing TiO₂-containing slag into a reaction zone of a reactor; andsupplying fluidizing gas comprising chlorine gas to the reaction zone tocause the following reaction within the reaction vessel:TiO₂+2Cl₂+C→TiCl₄+CO/CO₂, wherein the fluidizing gas is supplied viacenter nozzles formed through a central portion of a reactor base andfurther via rim nozzles formed through a rim of the reactor base thatsurrounds the central portion, wherein the fluidizing gas supplied viathe central nozzles is supplied at a first linear fluidizing velocitywhereas the fluidizing gas supplied via the rim nozzles is supplied at asecond linear fluidizing velocity that is higher than the first linearfluidizing velocity.
 13. The method of claim 12, wherein the rim of thereactor base is substantially horizontal, wherein the plurality of rimnozzles are formed through the substantially horizontal rim forsupplying fluidizing gas directly into the reaction zone above the rim,wherein the center of the reactor base is substantially horizontal,wherein the plurality of center nozzles are formed through thesubstantially horizontal center for supplying fluidizing gas into thereaction zone above the center via the collection zone.
 14. The methodof claim 13, wherein the center is stepped down from the rim, wherein asurface connecting the center and the rim comprises a portion that isgenerally perpendicular to the center.
 15. The method of claim 13,wherein the rim is peripheral to the center of the reactor base whenviewing the reactor base in a direction perpendicular to the center. 16.The method of claim 12, further comprising discharging at least part ofagglomerated particles settled in the collection zone eithercontinuously or intermittently.
 17. The method of claim 16, furthercomprising temporarily storing the agglomerated particles from thecollection zone.
 18. The method of claim 16, further comprisingsupplying purge gas for use in stripping chlorine gas.
 19. The method ofclaim 16, wherein the agglomerated particles contain molten alkalineearth metal chlorides.
 20. The method of claim 19, further comprisingmaintaining the molten alkaline earth metal chlorides at a concentrationbetween 5 wt % and 20 wt %.